SM Pro PR8 Mic Preamps

[bubba_b]

Has anyone checked out the TB-202? It's SMPro's dual channel strip (tube mic pre/opt. comp/eq). Just curious if there's any good mods for it as well (hopefully in the EQ section). I have one and it's decent for only $200, but I know it could be better and would like to make it so, if reasonable. If anyone would like pics to help out, just holla. :grin:

 

[SonsOfThunder]

[quote author="bubba_b"]like pics to help out, just holla.[/quote]

AAAAAAAAAAAAA!

But start a new thread, please.
Charlie

 

[ohhey]

[quote author="hairyandy"]Sorry I took so long with this guys...
....

Later...[/quote]

So what do these graphs look like for a good preamp ?

 

[meblumen]

Sorry for the dumb questions, I'm new to all of this but thank you very much for your help, patience and understanding. Much appreciated.

 

[bubba_b]

Sons,

Started a new thread on the TB202. Here's the link.

 

[GaryMedia]

At long last (after 28 business trips) I've been able to settle down to work the PR8 project again. I have the NE5532 opamps in there, and C13/14/15 are gone. It works.

I have two (2) Cinemag CMOQ-2H (hi-nickel core) output transformers and six (6) Cinemag CMOQ-2S (steel core) transformers ready for installation in the PR8 to displace the rear opamp/balancing board. Everything fits, but I'm reluctant to start the integration process.

Basically, I'm stuck with two issues:
(1) whether to use a 47uF low ESR capacitor between the output of the NE5532 and the primary of the transformer...or is it better to simply put a 100-ohm resistor in series with the primary?
(2) Should I simply stop where I am, sell the virgin tranformers (uncut leads) on the Black Market forum or eBay and buy an M-Audio Octane?

 

[SonsOfThunder]

[quote author="GaryMedia"]At long last...I have the NE5532 opamps in there, and C13/14/15 are gone. It works.[/quote]And how does it sound vs stock?

Everything fits, but I'm reluctant to start the integration process.

Why? Afraid you are going to "ruin" a $99 mic pre?

whether to use a 47uF low ESR capacitor...or is it better to simply put a 100-ohm resistor in series with the primary?

Depends on how much offset you have at that point in the ckt and how well that trafo will tolerate DC. When in doubt, use the cap!

Should I simply stop where I am...and buy an M-Audio Octane?

And how good is the Octane? and where is the DIY fun in that? Go for it!!

Peace!
Charlie

 

[hourglass]

Hey guys... my first post here after reading tons and tons of threads trying to get a handle on this stuff.

Anyhow, I found one of these PR8 preamps at the local used emporium for cheap and started looking for info. I think this thread is miles beyond what I ever could have hoped for - so thanks for all the tips and the in-depth circuit analysis.

Thus far I have chopped the three caps out of the input side of channels 2-8. I'm leaving channel 1 stock for the time being for comparisons.

I got some TI samples - they are NE5532APE4 chips.

I have no idea what all the letters & numbers on the ends of these things mean. I have managed to glean from other threads that a "DD" designation on some brands denotes low noise. I dunno about the TI stuff since I can't find any way to decipher it on their site.

Anyhow, I have socketed two channels (both the input and output boards) with the NE5532's. They sound very beefy to me - lots of low end. This seems to go against the "typical" sound of a 5532 as I understand it from other threads.

Now, my questions:

Should I have replaced both the input and output chips? I think so.
Is there a different TI 5532 or some other 5532 that might sound better in this particular circuit?
How many upgraded chips can the power supply in this box handle?
As in - can I put in 16 NE5532's without a problem? Can I put in 16 OPA2134's without a problem? Or if not, where should I draw the line?

I just noticed that I missed the deal about shorting C5 on the output board - what kind of difference does this make?

And finally - I've got some samples. They're nothing spectacular - just me kind of humming into a mic and then playing some guitar.

The singing alternates 2x thru one channel then 2x thru the other a few times for the most part. The guitar is 1x thru one channel and 1x thru the other channel.

See if you can spot which one is the stock channel (minus the 3 input caps) and which is the channel with the NE5532.

Sample is here:

http://www.ryanadam.com/halaka/mic.WAV

It's a mono wave file. I'm pretty sure it's 24-bit. The vocal is an SM-57. The guitar is a Sennheiser e609. Converter is an Apogee Rosetta AD.

ryan

 

[SonsOfThunder]

[quote author="hourglass"]Hey guys... my first post here.[/quote]Welcome to the forum...sorry about yer new addiction... I mean congrats on a new hobby!!

NE5532APE4

E4 = Lead free
P = DIP8 package
A = slightly better spec'd part, I think. Look at the data sheet.

Now, my questions:

Should I have replaced both the input and output chips? Is there a different TI 5532 or some other 5532 that might sound better in this particular circuit?

Yes, and I think that different opamps will have more and bigger differences than you'll find among 5532, though some might disagree.

How many upgraded chips can the power supply in this box handle?

As I have said before in this thread, I have two boxes: one has all Signetics 5532 and one has all OPA2134. Both are nice but a little different...not a lot really.

I missed the deal about shorting C5

Just one more part you can eliminate from the signal path.

And finally - I've got some samples...

I won't be listening to that 15MB sample on my crappy slow dialup here at home!

HTH!
Charlie

 

[jkokura]

[quote author="hourglass"] Should I have replaced both the input and output chips? I think so.

I just noticed that I missed the deal about shorting C5 on the output board - what kind of difference does this make?

And finally - I've got some samples. They're nothing spectacular - just me kind of humming into a mic and then playing some guitar.

See if you can spot which one is the stock channel (minus the 3 input caps) and which is the channel with the NE5532.

ryan[/quote]

My guess is that the first sample of both the vocal and the guitar is the mod with the new NE5532's...

Ok, so on to what I want to do to my PR8. I'm planning on cutting out C13, C14 and C15, and I want to figure out how to take out C10 as well... I know I just cut out C13/14/15, but with C10 do I need to solder in a short wire where the leads of C10 used to be? I'm taking C10 out becuase I'd rather do all my modding on the pre board so as to leave the output circuit as intact as I can (maybe later I'll entirely replace the pre board and use the existing output board... who knows.

2nd I want to replace the Opamps... Charlie, you answered the last post by saying that the 5532 and the 2134 will give you slight differences, but nothing too spectacular. What I'd really like to do is mod 4 of the pres with one IC and use another IC for the other 4. It's just something I think would give me more variety when I use these. Do you think this is a dumb idea? I know you've modded your two with identical IC's in each but different from each other...is it worth it to make all 8 the same? What about doing something like 2 pres with OPA2134, 2 with OP275, 2 with OPA2604 and 2 with NE5532 (I got all those chips from reading through this board - it seems like those are the ones being used here - I honestly don't have a clue how they're different from each other cause I'm a real newbie here, so I'm just throwing out the numbers after I searched mouser and found I can get all the IC's from there.)

Someone said they're IC's came as "TI samples"...what does that mean? Does that mean they got some to use free from a supply company? How could I get them like that? I don't want to shell out 3.15 a piece for the OP2134's I found on Mouser if I can get some free... I'm in Canada too if that makes a difference. Otherwise, where could I get them.

One last thing... How many IC's do I need per channel? I opened up my box and found a whole bunch of 4558's - two per channel. 1 is on the input board and 1 is on the output board. I kinda have the idea that replacing both would be best...do they have to be the same chip? Could I use OP2134's on the input side and 5532's on the output side and what would this sound like compared to using the same for input and output? Also, correct me if putting a socket in means I can just plug the IC in and take it out without soldering...What would be the advantage of doing this? Would it allow me to 'hotswap' the IC's kinda like changing tubes in mics/pres to get a differenct flavour? I'd rather not make it too complicated and would therefore prefer to simply solder the new IC's into place - is this more complicated?

Also, I have the older 'blue face' PR8...I've seen the black ones and they're much sexier...does this mod apply to both or just the new one or what?

Thanks for all the help - reading this has been a night of fun and excitement for me!

jacob

 

[SonsOfThunder]

Sorry for the delay in response...I forgot about this.

solder in a short wire where the leads of C10 used to be?

Yes.

mod 4 of the pres with one IC and use another IC for the other 4.

Cool.

What about 2 pres with OPA2134, 2 with OP275, 2 with OPA2604 and 2 with NE5532

I think you'll find some differences and some similarities.

"TI samples"...what does that mean?

Samples means samples. You can sometimes get companies to send samples for free. I would not encourage you to give any misleading information in order to get them free though.

How many IC's per channel? - two per channel.

You answered the question yourself. Smart guy that you are! :razz: :razz:

putting a socket in means I can just plug the IC in and take it out without soldering? Would it allow me to 'hotswap' the IC's?...is this more complicated?

Hotswap is not the correct term - that means that you can swap without turning anything off...NOT recommended!! You can change ICs at will (with the power off.), allowing experimentation without repeated soldering which can QUICKLY lead to destruction of the PCB. I used machine pin sockets on mine. Don't use cheap sockets!!

Also, I have the older 'blue face' PR8

I believe that the elimination of the C13/14/15 was implemented for the blackface PR8 (not PR8E) units. There are no reference designators on the PCB. I just made those up for discussion purposes. So you'll have to do some investigation on your unit to determine if it applies. Or post a pic of the internals!

Supposedly, the new PR8E has an "all new circuit"...?

Peace!
Charlie

 

[jkokura]

Also, I have the older 'blue face' PR8

I believe that the elimination of the C13/14/15 was implemented for the blackface PR8 (not PR8E) units. There are no reference designators on the PCB. I just made those up for discussion purposes. So you'll have to do some investigation on your unit to determine if it applies. Or post a pic of the internals!

Supposedly, the new PR8E has an "all new circuit"...?

Peace!
Charlie

Thanks a tonne Charlie, you've answered all my imperitive questions! I appreciate it.

Looking at the pictures posted above and looking at my PR8 internals I see no differences. Out of curiousity, Are you PR8's blue or black on the front? The Blue one I have only has the Phantom buttons on the front...no phase on the back, and as far as I can tell it's the original version that all the new SMPro "PR8 line" comes from...

Jacob

 

[SonsOfThunder]

Mine are both blue. I bought them just when the price dropped from $199 to $99. :grin: :grin: :grin:

The phase switch is only on the back of the PR8E, I think.

HTH!
Charlie

 

[87w]

Reviving an old topic here. There used to be pics in this thread that showed which caps to snip. They seem to have disappeared. I've poked around my unit and think I know which ones, but was hoping to verify before getting out my wire cutters. Anybody have a copy of that photo on their computer? Care to share it with me?

Sam

 

[SonsOfThunder]

Hmmm...

I think I still have that on another machine. I'll try tofind and repost on the server.

Sorry!

 

[thermos]

That would be great to get a pic of what caps to snip. They are still putting some of those in the PR8E (different values, but similar redundancy).

I had my tech put a bunch of different chips in the PR8E to try. The unanimous winner: the LT1358CN8. Super silky and not harsh at the same time, much better response than any of the burr browns we tried. I'm getting 2 units done with those.

 

[SonsOfThunder]

Is it the same board in the PR8E? Maybe you cannot tell since the pic is not online. I am having trouble finding the pics on any of my PCs...?

Still looking!
Charlie

 

[aortizjr]

Just some additional info.

I just bought a new PR8. Not the the E, just the regular black-face PR8. I got it from Musicians Fried for $99. I used their free shipping which was nice.

Anyway, earlier in this thread it was stated that SM Pro was going to make the capacitor cuts. They did not. Also the OpAmps are JRC4558's and the manual still states JRC4580.

The schematic posted seems to be right on. I didn't do a full trace, but it wasn't too bad to find the right places to clip.

I forgot about C10 and putting a jumper. So I didn't check to see if those two capacitors were there. So far I clipped C13,C14,C15. Then I put sockets for all the OpAmps and put an assortment of OpAmps in there to test out. It all works but I haven't had the time to compare differences in depth. So far the different OpAmps have very subtle differences. But just the capacitor clips make a really big difference.

With this you can only polish a terd so much... so I don't think I will be putting too much high quality stuff in this.

But here in the US, a 1U chassis 8" deep is around $50 + shipping. Add the 8 XLR and TRS connectors, transformers, heat sinks, etc. You are over the $100 most likely. So I might be buying more, design a new PCB that matches the layout. Then just take the nicely cut chassis, connectors, and maybe the dual transformers.

 

[thermos]

You guys have all tried changing the input and output caps, right? They are a very small value, something like 40 microferets or something. They aren't going to sould like anything unless the value is at least 100. With good input and output caps, new chips, and those uesless caps snipped the pres sound pretty good. I have a Great River and a Neve portico to compare. Its obviously not on the same level, but suprizingly good nevertheless.

 

[SonsOfThunder]

@aortizjr
Could you possibly take pics of your unit to show the caps to snip-snip? I have not been able to find my photos anywhere.

As I have said before, they are pretty darn good for the $ involved. Glad you guys also enjoy.

Curious to know which OAs you guys chose!

Peace!
Charlie